Properties of nanocrystalline TiO2 synthesized in premixed flames stabilized on a rotating surface

The properties of TiO₂ nanoparticles synthesized using the flame stabilized on a rotating surface method (FSRS) are investigated. The method uses a laminar, premixed, stagnation flame, combining particle synthesis and film deposition in a single step. The current study examines the effects of flame properties on particle characteristics. Synthesized particles were characterized using X-ray diffractometry, Transmission Electron Microscopy and UV–vis spectrometry in order to quantify the effects of equivalence ratio and precursor loading on particle size, crystallinity and optical band-gap. Results show that flame stoichiometry significantly affects crystal phase, but it has little to no effect on particle size and light absorption band edge. In addition, precursor loading impacts both the particle size and the crystal phase. The study demonstrates the potential of the FSRS method for producing tailored nanoscale TiO₂ particles for a variety of applications.     

Influence of Morphological Homogeneity of Superspherical Gold Nanoparticles on Plasmonic Photothermal Heat Generation

The plasmonic photothermal (PPT) characteristics of gold nanostructures have been extensively investigated theoretically and experimentally due to their potential for use materials science and industry. The management of the size and shape of gold nanoparticles has been a key issue in the development of better solutions for PPT heat generation because their size and shape determine their resultant photothermal properties. However, the light absorption of gold nanostructures is mainly dependent on the wavelength and orientation of the incident light; hence, maintaining uniform size and shape is critical for achieving maximum photothermal energy. Morphologically homogeneous spherical gold nanoparticles, or super gold nanospheres prepared by slowly etching uniform octahedral gold nanoparticles, demonstrate better PPT heat generation compared with commercially available nonsmooth gold nanoparticles (GNSs). The PPT heating experiments show a maximum temperature difference of 5.7 °C between the super and ordinary GNSs with the same average maximum Feret's diameters, which result from the more efficient PPT heat power generation (20.6%) of the super GNSs. In an electromagnetic‐wave simulation, the super GNSs show lower polarization dependence and a 24.6% higher absorption cross‐section than ordinary GNSs.     

Experimental investigation of Marangoni convection in nanofluids

Onset of regular convection in nanoparticle doped isotropic and anisotropic fluids with one free surface under absorption of light with Gaussian distribution of intensity due to temperature dependence of surface tension coefficient is experimentally studied. It is shown that nanoparticles essentially increase the thermal conductivity of the mixture, which leads to decrease of the velocity of convective motion. Dependence of velocity of hydrodynamic motions on intensity of laser beam and concentration of nanoparticles is also studied.     

电化学刻蚀制备的荧光碳纳米颗粒

以纯石墨作电极、乙二胺四乙酸二钠溶液作电解液制备了具有荧光性质的碳纳米颗粒。利用紫外-可见分光光度计和荧光分光光度计分析了碳纳米颗粒的光吸收和荧光发射特征,利用透射电镜和电子能谱分析了碳纳米颗粒的尺寸、晶体状态和成分。结果表明,碳纳米颗粒仅有几纳米,呈分散状态;在325 nm附近具有强的光吸收并表现出强的蓝光发射特征。研究了电解质溶液的种类、浓度等对碳纳米颗粒荧光发射的影响,讨论了碳纳米颗粒的荧光发射机理。     

Internal segregation of nanoparticles irradiated by laser radiation

The effect of the removal of zinc from brass nanoparticles has been experimentally discovered upon irradiating their suspension in ethanol by laser radiation. The analysis of the absorption spectra of nanoparticles shows that brass nanoparticles are transformed to copper nanoparticles during irradiation. The results are interpreted in terms of the high-pressure-induced modification of the phase diagram of nanoparticles. This pressure is caused by, first, the small radius of nanoparticles and, second, the pressure of the surrounding-liquid vapors upon the laser heating of nanoparticles.     

Using localized surface plasmons to modify the optical properties and conformational rearrangements of organic dye molecules

Optical properties of the molecular layers of cyanine dyes and their modification in a nearby field of silver nanoparticles on a sapphire substrate are investigated experimentally. Enhancement of the fluorescence and absorption intensity of organic molecules in the presence of silver nanoparticles is observed. The results from photomodifications of the molecular layers’ absorption properties with and without the presence of silver nanoparticles are described.     

Integrating sphere study of the optical properties of aluminum nanoparticles in tetranitropentaerytrite

The dependences of the transmission coefficients and the sum of the transmission and absorption coefficients for light with a wavelength of 643 nm in compressed pentaerythritol tetranitrate (PETN) samples containing aluminum nanoinclusions (average radius of 50 nm) on the pellet thickness and the mass fraction of aluminum nanoparticles in it are studied with an integrating sphere. The light absorption and scattering in this system is simulated using the Mie theory and a radiative transfer equation. The depth profile of absorbed energy in a sample is shown to approximately obey the Bouguer-Beer law. The effective cross section of radiation absorption by aluminum nanoparticles, which takes into account both light absorption and scattering by an ensemble of nanoparticles, exceeds the geometrical cross section.     

Enhancing the linear absorption and tuning the nonlinearity of TiO2 nanowires through the incorporation of Ag nanoparticles

We report on the enhanced linear absorption and modified nonlinear absorption of TiO2 nanowires coated with Ag nanoparticles. Experimental results indicated that the coated Ag nanoparticles significantly increased the linear absorption of the nanostructures in the wavelength range of visible light. Z-scan experiments showed that when the excitation energy increased, the nonlinear absorption of the TiO2 nanowires changed from reverse-saturable absorption to saturable absorption. When Ag nanoparticles were coated on the TiO2 nanowires, the reverse-saturable absorption was significantly inhibited. The as-prepared nanostructures may find potential applications in the field of solar cells and all-optical switching.     

Au@碳球复合结构中Au颗粒位置调控光吸收

采用时域有限差分（FDTD）法研究Au纳米颗粒@碳球（AuNPs@CS）复合结构的光吸收控制。发现Au纳米颗粒@碳球复合结构中Au颗粒的位置可以控制复合结构光吸收。模型计算中选取两粒Au纳米颗粒以最佳深度（0 nm）嵌入碳球表面。当两粒Au颗粒球心与碳球球心夹角为22.5°和45°时,复合结构光吸收较单一碳球光吸收明显增强;当夹角为315°、270°、180°、90°时,光吸收增量逐渐减小;当夹角为337.5°时,光吸收量低于单一碳球。这一结果主要归因于Au纳米颗粒位置变化可引起表面等离子体光强度和光散射方向的变化。改变碳球表面Au纳米颗粒的数量和位置,可以进一步调节AuNPs@CS复合结构的光吸收。     

Substrate-Modulated Electromagnetic Resonances in Colloidal Cu2O Nanospheres

Dielectric nanoparticles are expected to complement or even replace plasmonic nanoparticles in many optical and optoelectronic applications, because they exhibit small absorption losses and support strong electric and magnetic resonances simultaneously. Dielectric nanoparticles need to be deposited on various substrates in many applications. Understanding the substrate effect on the electromagnetic resonances of dielectric nanoparticles is of great importance for engineering their resonance properties and designing optical devices. In this study, moderate-refractive-index cuprous oxide nanospheres with uniform sizes and shapes are synthesized. The scattering spectra and images of the nanospheres deposited on three types of substrates are analyzed experimentally and theoretically. When supported on indium tin oxide–coated glass slides and Si wafers, the color of the nanospheres varies from blue, cyan, green, yellow, orange and red, covering almost the entire visible region. When deposited on gold films, the electromagnetic resonances of the nanospheres redshift intensively and a new effective magnetic resonance mode appears. The enhanced Raman scattering reveals that large electromagnetic field enhancements are produced in the gap region between the nanosphere and the substrate. The results shed light on the manipulation of the electromagnetic responses of dielectric nanoparticles and the design of dielectric metamaterials in the presence of various substrates.     

Nonlinear susceptibility of a metal-dielectric nanocomposite caused by induced dipole-dipole forces between particles

The optical coefficients of a nonlinearity for a macroscopic ensemble of aggregates of metal nanoparticles that is caused by deformation of the spatial structure of clusters in a strong light field are calculated for the first time. For a continuous medium that consists of a nonabsorbing dielectric containing aggregated silver nanoparticles that do not possess an intrinsic optical nonlinearity, coefficients of nonlinear absorption are obtained in relation to the intensity and frequency of incident light. It is shown that, at intensities of up to a few megawatts per square centimeter, the addition to the absorption of a nanocomposite to be modeled is adequately described by a third-order nonlinearity. The magnitude and sign of the nonlinear absorption coefficient agree well with the previously obtained experimental data for aggregated silver and gold colloids under nanosecond excitation.     

Investigation of the optical characteristics of composite materials based on cadmium sulfide nanoparticles stabilized in a high-pressure polyethylene matrix

Composite materials based on cadmium sulfide nanoparticles in an inert dielectric matrix of high-pressure (low-density) polyethylene are experimentally studied. It is shown how the size and weight concentration of nanoparticles in the bulk of the stabilizing matrix affect the nanocomposite absorption. The experimental results are interpreted based on the two-flux Kubelka-Munk model.     

金属纳米颗粒对有机太阳能电池光吸收效率影响的研究

借助时域有限差分法,对几种常见金属纳米颗粒影响有机太阳能电池光吸收效率的因素及其内部物理机制进行了研究.首先对金属纳米颗粒激发局域表面等离子共振的场分布特点进行分析,对比其在电池不同功能层中对光吸收率的影响;其次基于米氏理论与电共振效应,得出金属纳米颗粒的结构参量对局域表面等离子共振位置及强度的影响规律,并以此进行优化设计.结果表明,具有高对称性形貌的金属纳米颗粒以小尺寸密堆积结构引入电池活性层,能够促进电池光吸收增强三倍以上.     

金属纳米颗粒对有机太阳能电池光吸收效率影响的研究

借助时域有限差分法,对几种常见金属纳米颗粒影响有机太阳能电池光吸收效率的因素及其内部物理机制进行了研究.首先对金属纳米颗粒激发局域表面等离子共振的场分布特点进行分析,对比其在电池不同功能层中对光吸收率的影响;其次基于米氏理论与电共振效应,得出金属纳米颗粒的结构参量对局域表面等离子共振位置及强度的影响规律,并以此进行优化设计.结果表明,具有高对称性形貌的金属纳米颗粒以小尺寸密堆积结构引入电池活性层,能够促进电池光吸收增强三倍以上.     

Collective plasmon resonances in monolayers of metal nanoparticles and nanoshells

The collective plasmon resonances in a monolayer formed by metal or metal-dielectric nanoparticles with dipole or quadrupole single-particle resonances are theoretically and experimentally studied. The extinction, scattering, and absorption spectra are calculated using an exact many-particle solution for the system of interacting particles. With increasing surface density of particles in the monolayer, the dipole resonance is suppressed, and the spectrum of the collective system is determined by the quadrupole plasmon only. It is shown that the selective suppression of the long-wavelength extinction band is caused by the collective suppression of the dipole scattering mode, whereas the short-wavelength absorption spectrum of the monolayer differs little from the single-particle spectrum. Using dark-field light and atomic force microscopy, the kinetics of self-assembling of nanoshells is studied. It is shown that the universal linear relation between the relative shift of the wavelength of the collective quadrupole resonance and the relative increment of the refractive index of the surrounding medium is implemented.     

Absorption electronic spectrum of gaseous FeO: in situ detection with intracavity laser absorption spectroscopy in a nanoparticle-generating flame reactor

Absorption measurement of a gas-phase iron oxide (FeO) electronic spectrum is reported for the first time. FeO was obtained in a methane/oxygen/nitrogen flame doped with iron pentacarbonyl and monitored via the 611-nm band of the orange system with intracavity laser absorption spectroscopy. The measured spectral range extends from 16,250 to 16,450 cm^?1 for the appropriate intracavity tuning element position. The presented measurements demonstrate sensitive detection of the gas-phase precursor, playing a key role in flame synthesis of iron oxide nanoparticles. The sensitivity of the intracavity technique does not depend on broadband cavity losses and allows conducting measurements in a highly scattering, particle-laden flame environment.     

Enhanced light absorption of TiO(2) in the near-ultraviolet band by Au nanoparticles

We propose a scheme to enhance near-UV band absorption of a rutile TiO(2) nanoparticle by placing Au nanoparticles in its neighborhood. The discrete-dipole approximation method was employed to calculate the absorption spectrum of pure rutile TiO(2) and that of TiO(2) mixed with Au nanoparticles. The results indicate that pure rutile TiO(2) has its maximum absorption located in the deep-UV band. With the existence of Au nanoparticles, a significant light harvesting effect occurs, and this maximum shifts to the near-UV band, where usual excitation wavelength falls.     

Evaluation of electrical and optical characteristics of ZnO/CdS/CIS thin film solar cell

In this study, device modeling and simulation are conducted to explain the effects of each layer thickness and temperature on the performance of ZnO/CdS/CIS thin film solar cells. Also, the thicknesses of the CIS and CdS absorber layers are considered in this work theoretically and experimentally. The calculations of solar cell performances are based on the solutions of the well-known three coupling equations: the continuity equation for holes and electrons and the Poisson equation. Our simulated results show that the efficiency increases by reducing the CdS thickness. Increasing the CIS thickness can increase the efficiency but it needs more materials. The efficiency is more than 19% for a CIS layer with a thickness of 2 μm. CIS nanoparticles are prepared via the polyol route and purified through centrifugation and precipitation processes.Then nanoparticles are dispersed to obtain stable inks that could be directly used for thin-film deposition via spin coating.We also obtain x-ray diffraction(XRD) peak intensities and absorption spectra for CIS experimentally. Finally, absorption spectra for the CdS window layer in several deposition times are investigated experimentally.     

银/二氧化钛核壳纳米颗粒对碲化镉纳米晶的荧光增强研究

利用新合成的复合纳米结构银/二氧化钛核壳纳米颗粒,研究了金属银纳米颗粒对碲化镉纳米晶层荧光的增强情况.结果表明,这种新型复合金属纳米结构能极大地增强发光纳米晶层的荧光强度.银/二氧化钛核壳纳米颗粒是以水合肼、硝酸银和四异丙氧基钛为原材料,利用胶体化学法在水溶液中合成.透射电子显微镜图片表明这种新合成的银/二氧化钛纳米材料基本上呈球形,有较为明显的核壳结构,中间黑色的核是银纳米颗粒,外层颜色较浅部分是二氧化钛壳层.另外,包裹二氧化钛壳层后,银纳米颗粒的表面等离子吸收带从409 nm红移至430 nm,也证实了这种新型核壳纳米材料的形成.将此合成方法得到的银/二氧化钛纳米颗粒和碲化镉纳米晶用旋转涂覆方法进行直接组合后,得到了银纳米颗粒对碲化镉纳米晶荧光的明显增强,并对其增强的物理过程进行了讨论.这种能够增强荧光团发光的新型复合银纳米结构将在发光器件、荧光成像、生物探测等方面具有一定的应用价值.     

Optical Resonances of the Systems of Nanoparticles with a Metallic Shell

Characteristic features of the formation of the plasma resonance absorption spectra of double-layer nanoparticles with a dielectric core and metal shell were investigated theoretically and experimentally. Two peaks of the surface plasma resonances were observed with the example of an AgI–Ag system. The model of the conductivity electron free path limitation suggested by Kreibig for describing the dimensional dependence of the optical constants of homogeneous spherical metal nanoparticles was extended to the case where metal is concentrated in the shell of the particle. It is established that allowance for the dimensional effect leads to a decrease in plasma resonance absorption and expansion, with the two-peak band structure being preserved. The influence of the metal shell granularity and the degree of the polydispersity of particles on the spectral position, halfwidth, and absolute value of absorption resonances was investigated.